Gear-shift control device and gear-shift control method for automatic transmission

Abstract

An ECT-ECU includes a circuit that calculates an oil temperature threshold on the basis of a signal input from one of an engine coolant temperature sensor, an engine intake air temperature sensor, and an AT hydraulic fluid temperature sensor if a signal for starting an engine of a vehicle is input thereto from an ignition switch, a circuit that detects an oil temperature on the basis of a signal input from the AT hydraulic fluid temperature sensor at intervals of a predetermined sampling time while the vehicle is running, and a circuit that controls an automatic transmission to prohibit a gear shift from fourth speed to fifth speed if a detected oil temperature is lower than the oil temperature threshold.

Description

INCORPORATION BY REFERENCE[0001]The disclosures of Japanese Patent Application No. 2002-091044 filed on Mar. 28, 2002 including the specification, drawings, and abstract is incorporated herein by reference in its entirety.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The invention relates to a control device for a vehicular automatic transmission and, more particularly, to a device for controlling an automatic transmission on the basis of a temperature of hydraulic fluid contained therein.[0004]2. Description of the Related Art[0005]As an automatic transmission to be installed in a vehicle, there has generally been employed a transmission that is constructed by combining a torque converter composed of a pump, a turbine, a stator, and the like with a multistage-type gear-shift mechanism connected to the turbine of the torque converter. This automatic transmission is usually equipped with a hydraulic circuit portion and a hydraulic control device as a main component....

AI Technical Summary

Benefits of technology

[0017]A control device as another aspect of the invention comprises a detecting portion for detecting a timing when an engine of the vehicle is to be started, an oil temperature detecting portion for detecting a temperature of hydraulic fluid contained in the automatic transmission, an intake air temperature detecting portion for detecting a temperature of intake air introduced into the engine, a storing portion for storing an oil temperature threshold corresponding to the temperature of intake air at the time when the engine is started, a calculating portion that calculates an oil temperature threshold on the basis of the intake air temperature detected by the intake air temperature detecting portion at a timing detected by the detecting portion, and a control portion for controlling the automatic transmission in such a manner as to prohibit a gear shift to a specific gear stage if the oil temperature detected by the oil temperature detecting portion is equal to or lower than the oil temperature threshold calculated by the calculating portion while the vehicle is running.

[0018]A control method corresponding to the control device comprises a detecting step for detecting a timing when an engine of the vehicle is to be started, an oil temperature detecting step for detecting a temperature of hydraulic fluid contained in the automatic transmission, an intake air temperature detecting step for detecting a temperature of intake air introduced into the engine, a preparing step for preparing in advance an oil temperature threshold corresponding to the temperature of intake air at the time when the engine is started, a calculating step for calculating an oil temperature threshold on the basis of the intake air temperature detected in the coolant temperature detecting step at a timing detected in the detecting step, and a control step for controlling the automatic transmission in such a manner as to prohibit a gear shift to a specific gear stage if the oil temperature detected in the oil temperature detecting step is equal to or lower than the oil temperature threshold calculated in the calculating step while the vehicle is running.

[0019]A control device as another aspect of the invention comprises a detecting portion for detecting a first timing when an engine of the vehicle is stopped and a second timing which follows the first timing and at which the engine of the vehicle is started next time, an oil temperature detecting portion for detecting a temperature of hydraulic fluid contained in the automatic transmission, a measuring portion that measures a time that elapses from the first timing to the second timing, a storing portion for storing an oil temperature threshold corresponding to the time, a calculating portion that calculates an oil temperature threshold on the basis of a time measured by the measuring portion at the second timing detected by the detecting portion, and a control portion for controlling the automatic transmission in such a manner as to prohibit a gear shift to a specific gear stage if the oil temperature detected by the oil temperature detecting portion is equal to or lower than the oil temperature threshold calculated by the calculating portion while the vehicle is running.

[0020]A control method corresponding to the control device comprises a detecting step for detecting a first timing when an engine of the vehicle is stopped and a second timing which follows the first timing and at which the engine of the vehicle is started next time, an oil temperature detecting step for detecting a temperature of hydraulic fluid contained in the automatic transmission, a measuring step for measuring a time that elapses from the first timing to the seco...

Problems solved by technology

If the frictional coupling elements abruptly shift from a released state to a coupled state during control, a gear-shift shock may be caused.

Hence, although the frictional coupling elements are coupled at a suitable timing when hydraulic fluid is at a relatively high temperature, hydraulic fluid is supplied to or discharged from the frictional coupling elements with delay if the hydraulic fluid reaches a relatively low temperature.

For this reason, there are some cases where the frictional coupling elements cannot be released or coupled at a suitable timing.

As a result, a gear-shift shock may be caused.

Hence, the sensor does not directly measure a hydraulic fluid temperature in the vicinity of an actuator or a valve that actually performs gear-shift control.

Furthermore, since the hydraulic circuit of the automatic transmission is structurally complicated, the hydraulic fluid temperature varies widely with location.

If the control device disclosed in the abovementioned publication is applied under such a circumstance, gear-shift control cannot be performed on the basis of oil temperatures in actual operating regions.

Therefore, a gear-shift shock may be caused.

Thus, a deterioration in responsiveness based on a clutch-to-clutch operation using a direct pressure is caused.

In such a control device as well, since prohibition of a gear shift cannot be controlled on the basis of an oil temperature in an actual operating region, the following problem is caused.

As a result, driveability and fuel consumption are adversely affected.

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